To detect leaks in refrigeration systems, it is customary to provide fluorescent tracer dyes to refrigerant lubricants. Formerly, the refrigerant of choice was Freon which tolerated petroleum-based lubricants, in particular mineral oil. However, environmental concerns about the ozone-depleting nature of Freon has required alternative Freon-free refrigerating and air-conditioning system, e.g., such as refrigerant gases sold under the tradenames R-134 and R-134a. Due to this change, special components, gaskets, seals, etc. are required, particularly in automotive applications. These systems are incompatible with petroleum-based lubricating systems.
Alternative lubricants for Freon-free system are polyalkylene glycols and polyol esters. These are marketed by various companies, e.g. under trade names of Castrol SW20, Castrol AC flush and Mobile EAL 22. Most recently polyol esters have become the lubricants of choice for the industry. Up to this point, however, satisfactory dye molecules, which have liquid stability as a concentrate, have not been available. Dye manufacturers have unsuccessfully attempted to fluidize Solvent Yellow 43, a dye which is used for use in plastics, but has insufficient solubility in refrigerant lubricants for leak detection purposes.
Due to the sensitive nature, both environmentally and functionally, of refrigeration systems, the industry desires a fluorescent liquid colorant soluble in polyol ester type lubricants without the use of co-solvents. Formulating with co-solvents, particularly of an aromatic nature, may or may not help the liquid of a solid dye, such as C.I. Solvent 43, but this does not meet the stringent requirements of the industry.
Published PMN for Morton Yellow 10160 describes compounds having the formulae: ##STR2##
U.S. Pat. No. 5,858,930, the teachings of which are incorporated herein by reference describes dyes useful for refrigerant lubricants having the general formula: ##STR3## wherein R.sup.1 and R.sup.2 are each independently selected from branched alkyl groups containing 7 to 8 carbon atoms and alkyloxyalkyl groups containing 4 to 24 carbon atoms. These compositions are found to be weaker than desired and less stable than desired.